<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <div id="app">
    <div>
      <input type="text" v-model.lazy="uname" /><span>{{tip}}</span>
    </div>
  </div>
  <script src="./vue.js"></script>
  <script>
    new Vue({
      el: '#app',
      data: {
        uname: '',
        tip: ''
      },
      methods: {
        checkUname(newVal) {
          this.tip = '校验用户名中'
          setTimeout(() => {
            if(newVal === 'admin') {
              this.tip = '用户名admin已注册'
            } else {
              this.tip = '用户名注册成功'
            }
          }, 2000)
        }
      },
      watch: {
        uname(newVal, oldVal) {
          this.checkUname(newVal)
        }
      }
    })
  </script>
</body>
</html>